When engines are started up, the spark plugs are supplied with electricity from an electrical power source in order to produce a spark which ignites a mixture of air and fuel in the engine. The spark is obtained from a capacitor which produces a high-voltage electrical discharge between the electrodes. Generally, all of the spark plugs are supplied with power by the same power source, the power source being capable of providing enough power to ignite several spark plugs simultaneously. In order to separately supply each spark plug with power, they are connected to the power source by a power-supply path that is separate from that of the other spark plugs.
Furthermore, the ignition device may be controlled by a control system, which sends the device requests to ignite one or more spark plugs by means of a signal circulating in an electrical connection. In aeronautics, high-power generators are for example controlled by electronic control systems of the FADEC type (full authority digital engine control). A FADEC is a multiple-channel computer which receives a limited amount of information from sensors, controllers, flight devices and the pilot. It analyzes these data and responds by sending control requests to the flight devices, in accordance with procedures stored in the FADEC.
In order to economize and to prevent wear of the spark plugs, it is advantageous to use a single spark plug at start-up, alternating the use thereof at each start-up.
U.S. Pat. No. 7,509,812 describes, for example, a device comprising a generator and a control system that is capable of managing the ignition of two spark plugs of the same engine. It in particular describes a method which makes it possible to ignite an engine using one first spark plug, and then to use a second spark plug to accelerate the engine to a rotational speed that is sufficient to maintain the ignited engine independently. A particular case in the method which is linked to a failure makes it possible to use the second spark plug to ignite the engine if the first spark plug is not operational.
In U.S. Pat. No. 6,195,247, the disclosure relates to an ignition circuit comprising two spark plugs, which has a control system comprising two channels which are connected to the ignition circuit by two double connections. Each channel is thus capable of managing the ignition of the two spark plugs, in order to ensure start-up against the risk of a malfunction of the other channel.
However, these devices use the control system to directly manage alternating the power supply to the spark plugs. The devices in particular need to use one channel of the control system for each of the paths for supplying the spark plugs with power, and this is disadvantageous for the control system, which is charged with managing other flight devices.